Several solid state circuit interruption devices have proven feasible for substantially reducing the magnitude of the arc that occurs between separating contacts within a protected circuit. The devices generally comprise a combination of semiconductor elements that are selected to transfer the interrupted current away from the separating contacts immediately upon contact separation.
One such device is described within U.S. patent application Ser. No. 610,947 filed May 16, 1984 entitled "Solid State Current Limiting Interrupter" in the name of E. K. Howell. This device basically consists of the parallel combination of a voltage controlled element and a current controlled element connected across the separating contacts. Immediately upon contact separation, the current is transferred away from the contacts first to the current controlled element and then to the voltage controlled element. The time delay between the instant of contact separation and the transfer of current away from the contacts is within a few microseconds. seconds. The arc that occurs during this short time period has minimal effect on state-of-the-art contact materials. These materials generally comprise a combination of silver and tungsten or tungsten carbide. The silver provides excellent electrical conductivity between the contacts when in a closed configuration and the tungsten provides protection against sputtering of the contacts during the contact arcing.
U.S. patent application Ser. No. 665,841 filed Oct. 29, 1984 now U.S. Pat. No. 4,583,146 entitled "Fault Current Interrupter" in the name of E. K. Howell provides the combination of a positive temperature coefficient element with a voltage controlled element across the separating contacts to substantially reduce contact arcing U.S. patent application Ser. No. 681,478 filed Dec. 14, 1984 entitled "Circuit Interrupter Using Arc Commutation" in the name of E. K. Howell employs a zener diode and triac to transfer the current away from the separating contacts over to the voltage controlled device. All of the aforementioned Patent Applications, which are incorporated herein for reference purposes, exhibit some finite time delay between the time of contact separation and the transfer of current over to the solid state interruption circuit. Should the occurrence of an arc be completely eliminated such that the contacts can become separated without deleterious arcing effects, however brief, both the size of the contacts and the cost of contact materials can be substantially reduced. The purpose of this invention is to describe a circuit which completely eliminates the occurrence of an arc between separating contacts both under ordinary circuit conditions as well as upon the occurrence of an overload condition.